The present invention relates to a proximity detector and a radiography system, and more particularly, to a proximity detector for detecting the proximity of a movable unit to a subject using proximity sensing and to a radiography system including the proximity detector.
Imaging systems, such as x-ray radiography systems, are typically positioned close to a patient or subject to be imaged in order to provide desired imaging information. One type of radiation imager is a mobile C-arm system. In the medical field, the mobile C-arm system may be used for general surgery, orthopedic procedures, pain management procedures, vascular procedures, and cardiac procedures, for example. Typically, the mobile C-arm has an x-ray source mounted at one end of a mainframe and a detector, such as an image intensifier, mounted at the other end of the mainframe. The mobile C-arm may be moved in relation to the object, such as a patient, to be imaged.
Motorized motion of any of the axes of a mobile C-arm system poses possible risks to the patient and to the imaging system and other equipment. It is desirable to prevent or minimize collisions between the mobile C-arm and the object. A possibility of collision exists whether the C-arm is moved through automated trajectory tracking or through direct user input from a user interface device. It is therefore desirable to prevent or minimize collisions when the mobile C-arm is controlled by both an external user and by an automated system. A method and system for preventing collision between a mobile C-arm and an object would be highly desirable.
Imaging systems typically use one of two types of anti-collision sensors: contact sensors and proximity sensors. A contact sensor may use a bumper. The contact sensor detects a change in pressure resulting when the bumper contacts the object.
A proximity sensor detects the presence of an object within a given distance from a movable part of the C-arm imaging apparatus. A proximity sensor may be a capacitive proximity sensor. Typically, a plurality of capacitive sensor plates are used. A multiplexor selectively electrically couples the sensor plates and a capacitive sensing processing unit. Conventional sensor systems may also incorporate shielding to prevent detection of components in the imaging apparatus.
Proximity detection may be enhanced using two additional electrodes. One electrode may be used as a receiver. The other electrode is used as a transmitter and attached to the face of the x-ray detector, such as an image intensifier. Proximity detection with the two electrodes is based on a radio frequency (RF) coupling between the transmitting and receiving electrodes.
Current proximity sensor systems use several sensor plates. The sensor plates are placed around the x-ray detector (e.g., image intensifier) and in the face of the detector. Scanning circuitry includes a multiplexor to accommodate the plurality of sensor plates. The scanning circuitry increases overhead on sensing circuitry for the imaging system. U.S. Pat. No. 5,651,044, to Klotz et al., relates to one such multi-plate proximity sensor system.
Additionally, proximity sending is currently performed using RF coupling with both a transmitter and receiver. Capacitance is detected by a change in an electromagnetic field created by the transmitter when an object passes near the transmitter.
Current proximity sensors are limited by the complexity of electronic circuitry. Complex, additional electrical circuitry impacts the cost, maintenance, and performance, for example, of the imaging system. Current sensor systems are also limited by distances between sensors and imaging system components. That is, operating constraints limit the distance between a proximity sensor and an image intensifier, for example. Additionally, current sensor systems are limited by the use of an electromagnetic field for proximity detection. Furthermore, capacitive proximity sensing has not been used with a mobile C-arm apparatus.
Thus, a need exists for an improved proximity sensing mechanism using capacitive sensing techniques on a mobile C-arm apparatus.